There is/are a group of people.

The answer is below

Explanation:

There is a group of people

the pronoun reference replaces a noun, but you have to make sure there's no room for confusion.

in the first sentence "her" could be referring to shely or to the sister. the answer there is "shelly called her sister and told her about the new baby."

in the second sentence "it" could be referring to the roof or the floor. the answer there is "since the roof leaks on the family room floor, we need to repair the roof."

16.) true

17.) true

18.) no information in the text

19.) false

20.) no information in the text